The present invention relates generally to polymeric implants. More particularly, the invention relates to an improved catheter incorporating antimicrobial metal atoms to create a bactericidal/fungicidal surface treatment on a tissue contacting surface.
Central venous catheters are indispensable tools in modem medicine. It has been estimated that over one-fourth of patients hospitalized in the U.S.A. receive treatments via central venous catheters. For example, catheters are used for quick delivery of nutrient fluids, chemotherapy, and accurate measurement of central venous pressure.
Despite their utility, a variety of complications are associated with catheter use. Such complications include air embolisms, catheter-related sepsis (CRS), clot formation at the catheter tip, cardiac arrhythmia, and injury to peripheral nerves or blood cells. Additionally, the use of polymeric catheters has brought with it an increase in reports of complications, such as thrombophlebitis and sepsis.
It has been estimated that catheter-related sepsis or CRS occurs at a rate of 6 to 8 per 1000 catheter days, with a mortality rate of 10 to 20%. The classically accepted cause of CRS is bacterial migration and colonization along the catheter from the skin entry site. Not surprisingly, most bacteria found to cause CRS, such as the Staphylococcus species, commonly populate the skin.
Replacing the catheter at frequent intervals during treatment is a potential solution to CRS. Unfortunately, since there is no way to make a diagnosis before removing the catheter, this often results in removal of sterile catheters. Furthermore, since additional catheterization is potentially traumatic, doctors prefer to avoid it. Replacing the catheter with a new one over a guidewire eliminates the necessity of additional catheterization, but there is not presently enough data to verify that this technique reduces infection.
Since CRS is believed to be caused by migration of bacteria from the skin, it was thought that the use of wound dressings and topical antibiotics would reduce CRS. One approach has been to use Opsite.TM. type dressings, comprising a clear adhesive-backed membrane which has been shown to discourage bacterial growth. While the Opsite.TM. type dressing has proved somewhat effective in reducing insertion site colonization and infection, its use has been associated with wound and system infection outbreaks, and it is still considered experimental. Topical antibiotics have also been used at the catheter insertion site, but results of these studies have been conflicting. In a few cases, there were actually increases of some bacterial and fungal strains with the use of certain antibiotics.
In another approach, some catheter manufacturers have resorted to coating the entire length of the catheter with an antimicrobial metal or metal salt. Such catheters, known for example, as Bioguard.RTM. or Arrowguard.RTM. coated catheters, function to prevent infections by leaching silver or similar metals into the tissue and interstitial spaces around the catheter, thereby creating a toxicity zone which inhibits microbial migration. One common silver salt used for such controlled release applications is silver sulphadiazine. When this salt is exposed to physiological conditions, silver or silver ions are released into the zone surrounding the device.
Yet another promising technique for reducing CRS is the application of a subcutaneous cuff. Typically, the cuff is made from a porous material such as polyester and is placed around the catheter in the subcutaneous tissue such that tissue can grow into it. The ingrown tissue anchors the catheter in place and serves as a barrier to bacterial migration from the skin. By inhibiting transdermal movement and providing a mechanical barrier, such cuffs discourage microbial migration. Polyester cuffs have been used as bacterial barriers for many years on devices such as Hickman.RTM. and Broviac.RTM. catheters. These cuffed catheters have been very successful in reducing infection, with incidence of infection reportedly down to one case per patient-year.
In addition to the Hickman.RTM. and Broviac.RTM. catheters, another cuff, the VitaCuff.RTM., available from Vitaphore Corporation, has been developed to further improve catheter performance. This cuff is made of silicone elastomer which incorporates a collagen sponge with a silver compound distributed throughout its matrix. The silver is meant to act as an antimicrobial agent to further reduce the incidence of infection associated with catheter use. The infection resistance provided by the silver is related both to its ability to leach and to its ability to interfere with cell metabolism. Since the VitaCuff.RTM. leaches silver or silver ions into a volume of tissue surrounding the cuff, the coming is effective only for a limited period of time, on the order of 4-6 weeks, or until the collagen sponge and the subordinate silver is substantially exhausted.
Accordingly, an object of the present invention is to provide an improved catheter having antimicrobial properties.
An additional object of the present invention is to provide an improved catheter having antimicrobial properties which do not substantially degenerate over time.
A further object of the present invention is provide a device which exhibits antimicrobial properties for a longer period of time and performs in a manner that does not vary substantially over time for long time periods, e.g., on the order of months, or longer.
Another object of the invention is to provide an improved catheter which incorporates a subcutaneous cuff having specific antimicrobial properties.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.